1. Field of the Invention
The present invention relates generally to pulse width modulated power supplies and more particularly to pulse width modulator circuitry having a gain inversely proportional to the supply voltage of the voltage converter.
2. Description of the the Prior Art
Pulse width modulation DC--DC converters are well known in the art. Modern products incorporating DC--DC converters, such as digital computers, must be designed to operate successfully and accurately over the wide range of supply voltages which the products will encounter in various countries around the world. Unless the manufacturer customizes his product for each country in which the product is sold, the converter must be capable of accepting supply voltage which vary by as much as a factor of 2 from one country to another. Prior art converters typically use "linearly ramped" modulators in which the modulator gain is independent of the duty cycle. Therefore, since the incremental gain of the power converter portion of the converter will vary with the level of the supply voltage, the converter will have different closed-loop gains for different supply voltage levels. This variation in gain means that the regulation performance of the converter will not be uniform across the entire range of anticipated supply voltages. For example, if, as is common, a converter is designed for optimum performance at the higher supply voltages, the regulation at lower supply voltages will suffer.
One known prior art switching regulator which incorporates a quad comparator integrated circuit modulator is shown on page 230 of Switching Regulators and Power Supplies with Practical Inverters and Converters (copyright 1976,TAB Books) by Irving Gottlieb. The Gottlieb modulator, like the typical modulator, is designed to have a substantially linear ramp and is, therefore, also subject to the problem of non-uniform gain.
This and other problems of the prior art are solved by the present invention.